1. Field of the Invention
This invention relates to a pressure production unit, an ink jet printer installing the pressure production unit, and a control method for an air pump drive source in the pressure production unit. In particular, the invention relates to an art for making it possible to eliminate air pressure variations based on manufacturing errors of an orifice and an air pump in a pressurized air supply system.
2. Background Art
Hitherto, various ink jet printers capable of printing text and images in ink of multiplex colors supplied from ink cartridges of multiple colors have been put to practical use. A recent ink cartridge has been configured as follows: Ink in a bag formed of a thin film is stored in an ink storage chamber. An air chamber is formed in a space outside the bag. When wiping nozzles by a wiper, positive pressure can be made to act on ink through the thin film by pressurized air supplied to the air chamber. The air supply system includes an air pump, a drive motor for driving the air pump, an air tube extending from the air pump, a plurality of branch passages from the air tube to a plurality of ink cartridges, a pressure regulator or a relief valve for pressure regulation connected to the air tube in the vicinity of the air pump, or an orifice, and the like.
For example, in an ink jet printer disclosed in Japanese Patent No. 2703647, an air supply system similar to that described above is provided. The air supply system includes a relief valve for pressure regulation, an outside-air temperature sensor for detecting an outside-air temperature, a pressure sensor for detecting the pressure of pressurized air in an air tube, and the like. To produce pressurized air before or after use of the printer, the drive voltage for driving a pump drive motor is corrected in response to the outside-air temperature detected by the outside-air temperature sensor.
In an ink jet record apparatus disclosed in JP-A-10-138506, an air supply system similar to that described above is provided. The air supply system includes a pressure regulator and a plurality of change-over valves placed in a plurality of branch passages. In an apparatus disclosed in U.S. Pat. No. 6,290,343, an air supply system similar to that described above is provided and includes a pressure relief valve and a pressure sensor.
Generally, to wipe the print head face by a wiper in an ink jet printer, it is common operation to wipe the print head face in a state in which pressure is added to ink by pressurized air and the ink is swollen from the tip face of nozzles to the outside. Incomplete wiping of the print head face will result in degradation of the print quality. To wipe the print head face, if the air pressure of the pressurized air is too high, ink leaks wastefully from the nozzles. On the other hand, if the air pressure is too low, the ink is little swollen from the tip face of the nozzles to the outside and thus ink droplets of different colors, foreign substances, etc., deposited on the nozzle tips cannot completely be wiped, thus adversely affecting the next printing.
To provide the air supply system of the ink jet printer described above with an orifice and regulate the air pressure through the orifice, the correlation characteristic between the orifice inner diameter and the air pressure in the number of revolutions of operation of one air pump is as shown in FIG. 15. As seen in FIG. 15, the smaller the diameter of the orifice, the higher the air pressure; in the orifice of a small diameter of about 0.5 mmφ or less, the change width of the air pressure relative to change in the diameter is very large. Thus, a manufacturing error of each orifice has a considerable effect on the air pressure. Moreover, manufacturing errors of each air pump and each drive motor also occur and have an effect on the air pressure of pressurized air supplied from the air pump.
In printers in related arts, to set the control characteristics of an air pump drive motor, characteristic data of one, two, or three representative pressurized air production modules (air pump, drive motor, regulator or relief valve, etc.,) is acquired by experiment, and the control characteristics of all printers of the same model are determined based on the characteristic data. In this method, however, the effect of variations caused by manufacturing errors of the pressurized air production modules cannot be added.
Japanese Patent No. 2703647 discloses technical philosophy of making a temperature correction because the air pressure of pressurized air changes depending on the outside-air temperature, but does not disclose any measures against variations caused by manufacturing errors of the pressurized air production modules.
On the other hand, to adopt a diaphragm air pump as an air pump, a mechanism for transferring rotation of a drive motor to the diaphragm through an eccentric cam is adopted, but vibration sound produced by vibration of the diaphragm which reciprocates also causes noise at the printing time.